Most modern vehicles are fitted with a brake booster which uses a vacuum chamber to increase the braking force supplied from the brake pedal to the brake master cylinder. The brake booster prevents the brake pedal from feeling heavy to the driver.
The brake booster requires a source of vacuum pressure in order to operate, which, in naturally aspirated engines, is often delivered exclusively by the inlet manifold. In some circumstances the vacuum supplied by the inlet manifold may be insufficient. This may be due to a large amount of torque being supplied by the engine, either for mechanical drive or to power auxiliary electrical systems in the vehicle. In this case the inlet throttle may be fully open and hence inlet manifold vacuum may be low.
In order to maintain the brake booster vacuum under conditions of low inlet manifold vacuum, an additional vacuum source may be used, such as a super aspirator. A super aspirator may take the form of a venturi duct connected between the intake duct and inlet manifold across the inlet throttle, e.g. bypassing the inlet throttle. The pressure difference across the throttle drives a flow through the venturi allowing a lower pressure to be generated within the venturi. This can in turn be used to provide a lower pressure (higher vacuum) in the brake booster vacuum chamber than could be supplied by the inlet manifold.
A shut-off valve may control the operation of the super aspirator, e.g. by selectively permitting flow to the super aspirator. The shut-off valve may be opened when insufficient vacuum is present in the brake booster and/or inlet manifold. The shut-off valve may be controlled by the engine's power-train control module and may normally be in a closed position unless activated.
If the super aspirator is not required for long periods of time and hence the shut-off valve remains closed, contaminants within the air such as oil, dirt, fuel or other deposits may build up on the shut-off valve and impair its performance or prevent it opening when the super aspirator is required.
According to an aspect of the present disclosure, there is provided a method of cleaning a brake booster aspirator shut-off valve, the shut-off valve being operable to selectively permit flow of intake air through an aspirator, the aspirator bypassing a throttle of an engine and providing a vacuum source for a brake booster, wherein the method comprises: determining whether the shut-off valve may require cleaning; and at least partially opening the shut-off valve so as to permit a flow of air through the shut-off valve and clean the shut-off valve. The method may further comprise adjusting the throttle position of the engine to compensate for the additional flow of intake air through the aspirator.
The method may further comprise shutting the shut-off valve and returning the throttle to its unadjusted position. The opening and closing of the shut-off valve, together with the corresponding adjustments to the throttle position may be repeated, e.g. immediately repeated in a particular cleaning cycle, e.g. a predetermined number of times.
The throttle position may be adjusted to compensate for the additional flow of intake air through the aspirator in order to maintain a constant inlet manifold pressure. Additionally or alternatively, the throttle position may be adjusted to compensate for the additional flow of intake air through the aspirator in order to maintain a constant engine torque.
The method may further comprise: determining whether a possible change in throttle position can compensate for the additional flow of intake air through the aspirator. If a change in throttle position cannot compensate for the additional flow of intake air through the aspirator, cleaning of the shut-off valve may be delayed, e.g. for a set period of time or until the throttle position can compensate for the additional flow of intake air. Additionally or alternatively, the throttle position may be monitored and the shut-off valve may be cleaned when a change in throttle position can compensate for the additional flow of intake air through the aspirator.
The method may further comprise: determining whether the engine speed and/or torque is within a range in which cleaning of the shut-off valve is permitted. Cleaning of the shut-off valve may only be permitted if engine conditions are suitable. If the engine speed and/or torque is not within a range in which cleaning of the shut-off valve is permitted, cleaning of the shut-off valve may be delayed, e.g., for a set period of time. Additionally or alternatively, the engine speed and/or torque may be monitored, and the shut-off valve may be cleaned when the engine speed and/or torque is suitable.
Determining whether the shut-off valve may require cleaning may comprise determining an interval of: engine running time; engine revolutions; and/or engine or vehicle mileage; since the shut-off valve was previously opened and comparing the result to a predetermined threshold value. Additionally or alternatively, determining whether the shut-off valve may require cleaning may comprise determining an interval of time since the shut-off valve was previously cleaned and comparing the result to a predetermined threshold value. Again additionally or alternatively, determining whether the shut-off valve may require cleaning may comprise: sensing whether contaminants have built up within the aspirator shut-off valve. According to another aspect of the present disclosure, there is provided a method of cleaning a throttle, the throttle being operable to selectively permit flow of intake air into an inlet manifold of an engine, wherein the method comprises: determining whether the throttle may require cleaning; adjusting the position of the throttle so as to disturb any contaminants which have settled on the throttle; and adjusting the position of a super aspirator shut-off valve to compensate for the change in flow of intake air through the throttle, the super aspirator shut-off valve selectively permitting the flow of intake air through an aspirator bypassing the throttle.
According to another aspect of the present disclosure, there is provided a system for cleaning a brake booster aspirator shut-off valve or a throttle of an engine, the shut-off valve being operable to selectively permit flow of intake air through an aspirator, the aspirator bypassing the throttle of the engine and providing a vacuum source for a brake booster, wherein the system comprises one or more controllers, including executable instructions stored in memory, configured to perform the method according to any of the previously mentioned aspects of the disclosure.
The system may further comprise one or more sensors configured to sense whether contaminants have built up within the brake booster aspirator shut-off valve and/or throttle.
According to another aspect of the present invention, there is provided software, which when executed by a computing apparatus causes the computing apparatus to perform the method according to any of the previously mentioned aspects of the disclosure.
According to another aspect of the present invention, there is provided a vehicle or engine comprising the system for cleaning a brake booster aspirator shut-off valve or throttle of an engine according to any of the previously mentioned aspects of the disclosure.